Easy;  Someone writes up a "How to run this off an AC to DC adapter, by
adding a power socket" web page, then someone who doesn't know what
they're doing sticks a 48VDC 300 mA power lump into that socket, blowing
things up if not protected.  (I've seen this done, sadly;  Also quite
often just "any handy power lump that fits" is assumed to work just
fine, a Zener is a GOOD idea, so's the FET.)

An idea on this:  How about a Unidirectional TVS (Transient Voltage
Suppressor) instead of a Zener?  They're fast, cheap, and have pretty
high peak power ratings;  I am not sure what their average power ratings
are, which is why I'll ask if anyone knows what average power rating a
600W TVS will handle - anyone?  I can just cook one to destruction, I
suppose <G>  (Also:  I need the spice models for these, both uni- and
bi-directionals;  if anyone has those handy, it'd be nice!  Off-list, of
course <G>)

  Mark  (about 1/2 here today.)

Harold M Hallikainen wrote:
>
>         Yes, an even better idea!  I had not thought of that for this
> application, but it sounds good.  In the products I've done, I don't know
> how someone could stuff more AA cells in there than I had designed for,
> but SOMEONE could overvoltage it!
>
> Harold
>
> Harold Hallikainen
> harold@hallikainen.com
> Hallikainen & Friends, Inc.
> See the FCC Rules at http://hallikainen.com/FccRules and comments filed
> in LPFM proceeding at http://hallikainen.com/lpfm
>
> On Mon, 8 Nov 1999 08:14:03 -0800 Nick Taylor <ntaylor@INAME.COM> writes:
> >Harold's suggestion is good, but it can be improved by using an
> >appropriate valued zener for the diode ... also gives overvoltage
> >protection.  It's saved my breadboard circuits from frying more
> >than once.
> > - Nick -
> >
> >Harold Hallikainen wrote:
> >>
> >>         How about a series PTC then a shunt diode.  The diode will
> >conduct if
> >> the batteries are put in backwards, opening the PTC.
> >>
> >> Harold
> >>
> >> On Mon, 8 Nov 1999 05:26:07 -0800 mazzoni michele
> ><mazzoni@TECHEMAIL.COM>
> >> writes:
> >> >Hello List,
> >> >
> >> >I have realized an alarm for my bycicle using a 12C508. It is
> >powered
> >> >by two AA
> >> >size alkaline battery.
> >> >
> >> >I would like to know if there is a simple (and economic!!) solution
> >> >which
> >> >I can use to protect my circuit against polarity inversion during
> >> >battery change.
> >> >(I know it's a remote possibility, but it exists)
> >> >
> >> >I thought to use a serie diode, but the voltage drop bring the PIC
> >> >power voltage
> >> >near the power supply limit of the MCU.
> >> >
> >> >Thanks.
> >> >
> >> >
> >> >Best regards,
> >> >Michele
> >> >
> >> >_______________________________________________________
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